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Applies more rigorous logic to deciding when to stop parsing.

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This commit is contained in:
Thomas Harte 2019-07-16 18:06:54 -04:00
parent c123ca1054
commit 79a624e696
1 changed files with 18 additions and 7 deletions
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25
Storage/Disk/Encodings/AppleGCR/SegmentParser.cpp
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@ -52,14 +52,17 @@ std::map<std::size_t, Sector> Storage::Encodings::AppleGCR::sectors_from_segment
std::array<uint_fast8_t, 8> header{{0, 0, 0, 0, 0, 0, 0, 0}}; std::array<uint_fast8_t, 8> header{{0, 0, 0, 0, 0, 0, 0, 0}};
std::array<uint_fast8_t, 3> scanner{{0, 0, 0}}; std::array<uint_fast8_t, 3> scanner{{0, 0, 0}};
// Scan the track 1 and 1/8th times; that's long enough to make sure that any sector which straddles the // Scan the track while either all bits haven't been seen yet, or a potential
// end of the track is caught. Since they're put into a map, it doesn't matter if they're caught twice. // sector is still being parsed.
const size_t extended_length = segment.data.size() + (segment.data.size() >> 3); size_t bit = 0;
for(size_t bit = 0; bit < extended_length; ++bit) { int header_delay = 0;
while(bit < segment.data.size() || pointer != scanning_sentinel || header_delay) {
shift_register = static_cast<uint_fast8_t>((shift_register << 1) | (segment.data[bit % segment.data.size()] ? 1 : 0)); shift_register = static_cast<uint_fast8_t>((shift_register << 1) | (segment.data[bit % segment.data.size()] ? 1 : 0));
++bit;
// Apple GCR parsing: bytes always have the top bit set. // Apple GCR parsing: bytes always have the top bit set.
if(!(shift_register&0x80)) continue; if(!(shift_register&0x80)) continue;
if(header_delay) --header_delay;
// Grab the byte. // Grab the byte.
const uint_fast8_t value = shift_register; const uint_fast8_t value = shift_register;
@ -86,6 +89,8 @@ std::map<std::size_t, Sector> Storage::Encodings::AppleGCR::sectors_from_segment
new_sector->data.reserve(710); new_sector->data.reserve(710);
} else { } else {
sector_location = static_cast<std::size_t>(bit % segment.data.size()); sector_location = static_cast<std::size_t>(bit % segment.data.size());
header_delay = 200; // Allow up to 200 bytes to find the body, if the
// track split comes in between.
} }
} }
} else { } else {
@ -193,7 +198,9 @@ std::map<std::size_t, Sector> Storage::Encodings::AppleGCR::sectors_from_segment
break; break;
} }
} }
if(out_of_bounds) continue; if(out_of_bounds) {
continue;
}
// Test the checksum. // Test the checksum.
if(decoded_header[4] != (decoded_header[0] ^ decoded_header[1] ^ decoded_header[2] ^ decoded_header[3])) if(decoded_header[4] != (decoded_header[0] ^ decoded_header[1] ^ decoded_header[2] ^ decoded_header[3]))
@ -213,11 +220,15 @@ std::map<std::size_t, Sector> Storage::Encodings::AppleGCR::sectors_from_segment
break; break;
} }
} }
if(out_of_bounds) continue; if(out_of_bounds) {
continue;
}
// The first byte in the sector is a repeat of the sector number; test it // The first byte in the sector is a repeat of the sector number; test it
// for correctness. // for correctness.
if(sector->data[0] != sector->address.sector) continue; if(sector->data[0] != sector->address.sector) {
continue;
}
// Cf. the corresponding section of Encoder.cpp for logic below. // Cf. the corresponding section of Encoder.cpp for logic below.
int checksum[3] = {0, 0, 0}; int checksum[3] = {0, 0, 0};